A study published in JAMA Psychiatry indicates a significant link between cannabis use disorder (CUD) and the development of mental disorders. Researchers from Aarhus University and the University of Copenhagen analyzed data from Danish nationwide registers such as the National Patient Register, the Danish Psychiatric Central Research Register, and the Danish Register of Pharmaceutical Sales.
After reviewing over six million patient records, the researchers found evidence that CUD increases the risk of psychotic and non-psychotic depression and bipolar disorder. The study only focused on people registered with a substance use disorder and treated by the substance abuse treatment system or other parts of the Danish healthcare system. The study included men and women born in Denmark before 2006, and they lived in Denmark between 1995 and 2021.
Previous studies by the research team examined the association between cannabis and mental health disorders and suggested that CUD can increase the risk of schizophrenia. However, this study revealed that individuals with cannabis use disorder are at twice the risk of developing depression. Heavy cannabis consumers are two to three times more likely to develop bipolar disorder.
More research into the risks of CUD can strengthen preventative measures and identify risk factors for the transition from cannabis use disorder to psychiatric disorders. Some researchers believe this association is complex and suspect that circular feedback occurs when excessive cannabis use and emerging psychiatric symptoms coincide. Some individuals may use cannabis to manage mental health symptoms, but cannabis possibly exacerbates their mental health problems.
Analysis of Danish register data provides insights into many crucial factors that could affect CUD and increased risk of mental disorders, but it does not provide conclusive evidence. Further research and randomized controlled trials would provide a better understanding of this risk and inform cannabis regulation policy. Danish general practitioners have been able to write prescriptions for drugs based on cannabis for patients as part of a trial scheme since 2018. This scheme also permits companies and individuals the opportunity to produce cannabis for medicinal or industrial use.